This invention relates to a container for housing a large number of minute solder balls.
Multifunctional electronic components such as BGA""s, CSP""s, and the like are mounted on printed circuit boards by joining the leads to the lands of printed circuit boards with solder. Multifunctional electronic components have a large number of leads, and the leads are extremely small, so when solder is separately supplied at the time of soldering, not only is a great deal of labor required, but is not possible to accurately supply solder to minute portions to be soldered. Therefore, with multifunctional electronic components, solder is adhered to the leads in advance to form solder bumps, and at the time of soldering, the bumps are melted to perform soldering. Solder balls are used to form solder bumps for such multifunctional electronic components.
In general, with solder balls used for BGA""s, those having a diameter of 0.76 mm are most common, but with CSP""s, minute ones having a diameter such as 0.15 mm or 0.1 mm are used. These solder balls are placed in containers made of glass or plastic and are transported from the manufacturer to the consumer.
A method of forming solder bumps for multifunctional electronic components comprises coating the leads in the locations which are to soldered with a sticky flux, mounting solder balls on the regions which have been coated with flux using a mounting device and then performing heating with a heating device such as a reflow furnace, and then melting the solder balls to form solder bumps.
However, when forming solder bumps on multifunctional electronic components, problems occur such as inadequate adhesion in which the solder balls do not thoroughly adhere to the leads, or the region in the vicinity of where solder bumps are formed becoming dirty. As other problems, there were cases where failure of mounting took place in which solder balls could not be mounted at all on the portions of multifunctional electronic components where solder bumps were to be formed, or where over-mounting occurred in which a plurality of solder balls were mounted.
The present inventors performed an intensive study of the above-described problems, and as a result, it was found that the occurrence of inadequate adhesive strength or of the vicinity of the region where solder bumps are formed becoming dirty is due to the surface of solder balls becoming covered with black powder and becoming blackened, and the failure of mounting to take place or over-mounting of solder balls in the region where solder bumps are to be formed is due to solder balls becoming charged with static electricity.
Namely, when the surface of solder balls becomes blackened, the black powder becomes a hindrance to soldering at the time of soldering, and the solder balls do not completely adhere to leads, and even if solder balls which have become blackened adhere to leads, black powder which falls from the solder balls remains in the vicinity of the regions where bumps are to be formed and ends up making the regions dirty. In addition, if this black powder adheres to the regions between leads having a narrow pitch, poor insulation can result.
Furthermore, if solder balls become charged, there are cases in which due to static electricity, failure of mounting takes place, and they adhere to unnecessary locations. Solder balls are not mounted on the prescribed locations of an electronic device. In addition, if a plurality of solder balls end up adhering due to static electricity to a prescribed portion of a solder ball mounting jig, excessive mounting occurs, and a giant bump ends up being formed at the time of solder bump formation.
As shown in FIG. 1, an existing solder ball container (referred to below as a container) was made up of a body 1, an outer lid 2, and a middle lid 3. The body 1 was a cylindrical member with a bottom and was made of a transparent material such as glass or plastic, an opening 4 was formed in its upper portion, and a male thread 5 was formed on the outside of the upper portion.
The outer lid 2 is in the shape of a cap, and a female thread 6 which engages with the male thread 5 of the body 1 is formed on its interior.
The middle lid 3 is a cylindrical member having a shallow bottom, its outer diameter has approximately the same diameter as the opening 4 of the body 1, and a flange 7 is formed on its upper portion. The middle lid 3 seals the opening 4 by fitting of the flange 7 to the opening 4 of the body 1.
Next, a simple explanation will be given of the state in which solder balls are placed into the existing container.
As shown in FIG. 2, a prescribed amount of solder balls B (referred to below simply as balls) is placed into the body 1 of the container, the opening 4 is tightly sealed by the middle lid 3, and the opening 4 is sealed by the outer lid 2. At this time, a large gap K develops between the balls B and the lower surface of the middle lid 3. The reason why a container on the large size in which such a large gap can develop is used is so to be able to cope with increases or decreases in the volume of the balls. Namely, if the container is made on the large size, even if the overall volume of the balls is somewhat large, there is ample space and the balls can be accommodated. For example, balls with a diameter of 0.76 mm generally have a tolerance of xc2x10.02 mm. When a large number of balls of a large diameter on the + side of this tolerance is placed into a container, the overall volume of the balls increases. The volume of the balls themselves increases according to the cube of the increase in the diameter of the balls, so with a container without a gap, when a prescribed amount of balls of prescribed dimensions is placed into it, in the case in which there are a large number of large balls, the prescribed number of balls ends up not fitting in.
However, when a large number of balls of prescribed dimensions or smaller than the prescribed dimensions are placed into a container on the large size of this type, a gap K such as shown in FIG. 2 ends up being formed.
When a ball manufacturer places solder balls into a container in which a large gap develops after balls are placed into it and ships it to a consumer, during shipping, the balls are shaken or made to tumble within the container and rub against the wall surface of the container. As a result, the surface of the balls ends up becoming black, and the solder balls end up being charged with static electricity. Blackening or electrical charging of the balls ends up causing soldering defects, dirtying of the vicinity of solder bumps, and problems such as failure of mounting to take place or excessive mounting of balls, as described above.
Due to the fact that blackening or electrical charging of balls in this manner is caused by a large gap within a container, means for getting rid of the gap have been conceived. One means is to fill a gap which forms in a container with a packing. As a packing for preventing movement of balls, it has been proposed to crumple up sheets of paper or polyethylene or the like and to cram them into the gap. However, with a packing made from crumpled sheet material, balls ends up penetrating into gaps in the crumpled material, and when the packing is removed, balls fly out therewith and end up being scattered in the periphery.
As shown in FIG. 3, it has been conceived of packing with a packing P made of sponge. However, if the balls are pressed until the sponge packing gets rid of a gap, the solder balls continuously receive the elastic reaction from the packing, and with the passage of a prolonged period of time, soft balls made of tin or lead end up being deformed, and at the time of solder bump formation, they cannot be accurately mounted by a ball mounting apparatus, resulting in failure of mounting to take place.
The object of this invention is to provide a solder ball container which prevents blackening and charging with electricity and does not produce deformation during transport of solder balls which fill the container.
The blackening and charging with static electricity of balls is due to balls being shaken and tumbled during transport and rubbing against the wall surface of a container as described above. Namely, the blackening of balls is caused by the surface of the balls being scraped when the balls rub against the wall surface of the container, and fine solder powder falls from the surfaces of the balls. Solder powder has a large surface area, so it is easily oxidized and blackened, and it adheres to balls, or it adheres to the vicinity of solder bumps after soldering, and it produces an unsightly blemish. As for charging of balls with static electricity, balls which tumble within the container during transport rub the wall surface of the container and static electricity is generated, so the balls end up being charged.
The present inventors perceived that if balls which are placed in a container are not vibrated by a large amount or made to tumble during transport, blackening or electrical charging of balls can be prevented, and thereby created the present invention.
The present invention is a solder ball container in which the opening of a cylindrical body with a bottom is sealed by an outer lid, characterized in that a projection having a shape which will not deform solder balls when it is inserted into a plurality of solder balls packed into the container is installed in the opening of the container.